[Bug tree-optimization/47239] New: (int)&func & 3 is always optimized to 0 on some targets

["kkojima at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47239

           Summary: (int)&func & 3 is always optimized to 0 on some
                    targets
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: kkojima@gcc.gnu.org


Targets like arm, hppa and sh64 use the lower bits of the address
of functions for special purposes.  Even on those targets,

----
extern void plabel32_function (void);

int
is_plabel32 (void)
{
  return ((unsigned long) &plabel32_function & 3);
}
----

which was the test case of PR 35705, is wrongly compiled with -O2.
It seems that tree-bit-ccp optimization evaluates the expression
((unsigned long) &plabel32_function & 3) to zero always.
With -fno-tree-bit-ccp, the result looks OK.  For example, arm-eabi
compiler outputs

    mov    r0, #0
    bx    lr

with -O2 and

    ldr    r0, .L2
    and    r0, r0, #3
    bx    lr
.L3:
    .align    2
.L2:
    .word    plabel32_function

with -O2 -fno-tree-bit-ccp.  I've got similar results for hppa and sh64
compilers.